Here's the versions I'm working with.
Not sure I understand exaclty what you want to accomplish, but lets see if I can help out a little bit anyway.
You create custom tabs (as long as we're not talking Commerce Manager here) and add properties to it the same way as in CMS. See http://world.episerver.com/blogs/Per-Bjurstrom/2015/2/typed-tabsgroups/.
To add a selection of specification types you could add a property to your variation types, and connect an ISelectionFactory to it. That can be done either through an attribute, http://world.episerver.com/blogs/Linus-Ekstrom/Dates/2013/12/SingleMultiple-selection-in-EPiServer-75/, or an editor descriptor, http://www.kimgunnarsson.se/generic-editordescriptor-for-custom-selectionfactories/.
And then you could add more properties to your variation types to contain any other specification information, and also connect them to your custom tab. The only tricky part is if different specification fields should be loaded dynamically, depending on the specification type choice.
Sorry for waking up this ancient thread, but I'm facing the exact same issue. I'd like to create a custom tab for Commerce content (next to Assets, Related Entries, Belongs To, etc) but I don't want to define properties and and a tab group for it. I'd like to use "epi-cms/widget/IFrameController" as the controller type and make the tab load a separate page.
Is this possible? I've been digging for a while and the only thing I can find is to create my own ViewConfiguration and that works nicely. But view configurations are quite hidden, I'd really like to be able to use a tab for it.
In catalog ui, on all my variants, I'd like to create a Tab called "Specifications" that when clicked, opens up a custom properties panel that allows me to select from a list of specification types, then enter the values for the specifications that belong to that specific sku.
Could I get any advice on where to begin with creating a customer modification like this?